Biodegradation of benzene, toluene, and xylene (BTX) in liquid culture and in soil by Bacillus subtilis and Pseudomonas aeruginosa strains and a formulated bacterial consortium

Degradation of multiple PAHs and co-contaminants by microbial consortia and their toxicity assessment

The anthropogenic activities toward meeting the energy requirements have resulted in an alarming rise in environmental pollution levels. Among pollutants, polycyclic aromatic hydrocarbons (PAHs) are the most predominant due to their persistent and toxic nature. Amidst the several pollutants depuration methods, bioremediation utilizing biodegradation is the most viable alternative. This study investigated the biodegradation efficacy using developed microbial consortium PBR-21 for 2-4 ringed PAHs named naphthalene (NAP), anthracene (ANT), fluorene (FLU), and pyrene (PYR). The removal efficiency was observed up to 100 ± 0.0%, 70.26 ± 4.2%, 64.23 ± 2.3%, and 61.50 ± 2.6%, respectively, for initial concentrations of 400 mg L-1 for NAP, ANT, FLU, and PYR respectively. Degradation followed first-order kinetics with rate constants of 0.39 d-1, 0.10 d-1, 0.08 d-1, and 0.07 d-1 and half-lifet 1 / 2  of 1.8 h, 7.2 h, 8.5 h, and 10 h, respectively. The microbial consortia were found to be efficient towards the co-contaminants with 1 mM concentration. Toxicity examination indicated that microbial-treated PAHs resulted in lesser toxicity in aquatic crustaceans (Artemia salina) than untreated PAHs. Also, the study suggests that indigenous microbial consortia PBR-21 has the potential to be used in the bioremediation of PAH-contaminated environment.

Enhanced indigenous consortia for the remediation of uranium-contaminated groundwater by bioaugmentation: Reducing and phosphate-solubilizing consortia

To investigate the strengthening effects and mechanisms of bioaugmentation on the microbial remediation of uranium-contaminated groundwater via bioreduction coupled to biomineralization, two exogenous microbial consortia with reducing and phosphate-solubilizing functions were screened and added to uranium-contaminated groundwater as the experimental groups (group B, reducing consortium added; group C, phosphate-solubilizing consortium added). β-glycerophosphate (GP) was selected to stimulate the microbial community as the sole electron donor and phosphorus source. The results showed that bioaugmentation accelerated the consumption of GP and the proliferation of key functional microbes in groups B and C. In group B, Dysgonomonas, Clostridium_sensu_stricto_11 and Clostridium_sensu_stricto_13 were the main reducing bacteria, and Paenibacillus was the main phosphate-solubilizing bacteria. In group C, the microorganisms that solubilized phosphate were mainly unclassified_f_Enterobacteriaceae. Additionally, bioaugmentation promoted the formation of unattached precipitates and alleviated the inhibitory effect of cell surface precipitation on microbial metabolism. As a result, the formation rate of U-phosphate precipitates and the removal rates of aqueous U(VI) in both groups B and C were elevated significantly after bioaugmentation. The U(VI) removal rate was poor in the control group (group A, with only an indigenous consortium). Propionispora, Sporomusa and Clostridium_sensu_stricto_11 may have played an important role in the removal of uranium in group A. Furthermore, the addition of a reducing consortium promoted the reduction of U(VI) to U(IV), and immobilized uranium existed in the form of U(IV)-phosphate and U(VI)-phosphate precipitates in group B. In contrast, U was present mainly as U(VI)-phosphate precipitates in groups A and C. Overall, bioaugmentation with an exogenous consortium resulted in the rapid removal of uranium from groundwater and the formation of U-phosphate minerals and served as an effective strategy for improving the treatment of uranium-contaminated groundwater in situ.

In Situ Discrimination and Cultivation of Active Degraders in Soils by Genome-Directed Cultivation Assisted by SIP-Raman-Activated Cell Sorting

The identification and in situ cultivation of functional yet uncultivable microorganisms are important to confirm inferences regarding their ecological functions. Here, we developed a new method that couples Raman-activated cell sorting (RACS), stable-isotope probing (SIP), and genome-directed cultivation (GDC)─namely, RACS-SIP-GDC─to identify, sort, and cultivate the active toluene degraders from a complex microbial community in petroleum-contaminated soil. Using SIP, we successfully identified the active toluene degrader Pigmentiphaga, the single cells of which were subsequently sorted and isolated by RACS. We further successfully assembled the genome of Pigmentiphaga based on the metagenomic sequencing of 13C-DNA and genomic sequencing of sorted cells, which was confirmed by gyrB gene comparison and average nucleotide identity determination. Additionally, the genotypes and phenotypes of this degrader were directly linked at the single-cell level, and its complete toluene metabolic pathways in petroleum-contaminated soil were reconstructed. Based on its unique metabolic properties uncovered by genome sequencing, we modified the traditional cultivation medium with antibiotics, amino acids, carbon sources, and growth factors (e.g., vitamins and metals), achieving the successful cultivation of RACS-sorted active degrader Pigmentiphaga sp. Our results implied that RACS-SIP-GDC is a state-of-the-art approach for the precise identification, targeted isolation, and cultivation of functional microbes from complex communities in natural habitats. RACS-SIP-GDC can be used to explore specific and targeted organic-pollution-degrading microorganisms at the single-cell level and provide new insights into their biodegradation mechanisms.

Indene, indane and naphthalene in a mixture with BTEX affect aerobic compound biodegradation kinetics and indigenous microbial community development

BTEX (benzene, toluene, ethylbenzene, xylene) are common pollutants often found in former gasworks sites together with some other contaminants like indene, indane and naphthalene (Ie, Ia, N). This study aimed to evaluate the inhibitory or stimulative substrate interactions between BTEX, and Ie, Ia, N during aerobic biodegradation. For this, batch bottles, containing originally anaerobic subsurface sediments, groundwater and indigenous microorganisms from a contaminated former gasworks site, were spiked with various substrate combinations (BTEX, BTEXIe, BTEXIa, BTEXN, BTEXIeIa, BTEXIeN, BTEXIaN, BTEXIeIaN). Subsequently concentrations were monitored over time. For the BTEXIeIaN mixture, initial concentrations were between 1 and 5 mg L-1, and all compounds were completely degraded by the microbial consortia within 39 days of incubation. The experimental data were fitted to a first order kinetic degradation model for interpretation of inhibition/stimulation between the compounds. Results showed that indene, indane, and naphthalene inhibited the degradation of benzene, toluene, ethylbenzene, o-xylene, with benzene being the most affected. M/p-xylene is the only compound whose biodegradation is stimulated by the presence of indene and indane (individually or mixed) but inhibited by the presence of naphthalene. 16S rRNA amplicon sequencing revealed differentiation in the microbial communities within the batches with different substrate mixtures, especially within the two microbial groups Micrococcaceae and Commamonaceae. Indene had more effect on the BTEX microbial community than indane or naphthalene and the presence of indene increased the relative abundance of Micrococcaceae family. In conclusion, co-presence of various pollutants leads to differentiation in degradation processes as well as in microbial community development. This sheds some light on the underlying reasons for that organic compounds present in mixtures in the subsurface of former gasworks sites are either recalcitrant or subjective towards biodegradation, and this understanding helps to further improve the bioremediation of such sites.

Metagenomic analysis reveals specific BTEX degrading microorganisms of a bacterial consortium

Petroleum hydrocarbon contamination is of environmental and public health concerns due to its toxic components. Bioremediation utilizes microbial organisms to metabolism and remove these contaminants. The aim of this study was to enrich a microbial community and examine its potential to degrade petroleum hydrocarbon. Through successive enrichment, we obtained a bacterial consortium using crude oil as sole carbon source. The 16 S rRNA gene analysis illustrated the structural characteristics of this community. Metagenomic analysis revealed the specific microbial organisms involved in the degradation of cyclohexane and all the six BTEX components, with a demonstration of the versatile metabolic pathways involved in these reactions. Results showed that our consortium contained the full range of CDSs that could potentially degrade cyclohexane, benzene, toluene, and (o-, m-, p-) xylene completely. Interestingly, a single taxon that possessed all the genes involved in either the activation or the central intermediates degrading pathway was not detected, except for the Novosphingobium which contained all the genes involved in the upper degradation pathway of benzene, indicating the synergistic interactions between different bacterial genera during the hydrocarbon degradation.

Characterizations of highly efficient moderately halophilic toluene degrading exiguobacterium mexicanum M7 strain isolated from Egyptian saline sediments

Toluene and other monoaromatic compounds are released into the environment particularly saline habitats due to the inappropriate disposal methods of petroleum products. Studying the bio-removal strategy is required to clean up these hazardous hydrocarbons that threaten all ecosystem life using halophilic bacteria with higher biodegradation efficiency of monoaromatic compounds as a sole carbon and energy source. Therefore, sixteen pure halophilic bacterial isolates were obtained from saline soil of Wadi An Natrun, Egypt, which have the ability to degrade toluene and consume it as the only source of carbon and energy. Amongst these isolates, isolate M7 exhibited the best growth with considerable properties. This isolate was selected as the most potent strain and identified based on phenotypic and genotypic characterizations. The strain M7 was belonging to Exiguobacterium genus and founded to be closely matched to the Exiguobacterium mexicanum with a similarity of 99%. Using toluene as sole carbon source, strain M7 showed good growth at a wide range temperature degree (20-40ºC), pH (5-9), and salt concentrations (2.5-10%, w/v) with optimal growth conditions at 35ºC, pH 8, and 5%, respectively. The biodegradation ratio of toluene was estimated at above optimal conditions and analyzed using Purge-Trap GC-MS. The results showed that strain M7 has the potentiality to degraded 88.32% of toluene within greatly short time (48 h). The current study findings support the potential ability to use strain M7 as a biotechnological tool in many applications such as effluent treatment and toluene waste management.

Simultaneous biodegradation of dimethyl sulfide and 1-propanethiol by Pseudomonas putida S-1 and Alcaligenes sp. SY1: "Lag" cause, reduction, and kinetics exploration

Simultaneous biodegradation of malodorous 1-propanethiol (PT) and dimethyl sulfide (DMS) by Pseudomonas putida S-1 and Alcaligenes sp. SY1 was investigated and the interactions implicated were explored. Results showed that PT was completely degraded in 33 h, while a lag of 10 h was observed for DMS degradation alone, and the lag was even extended to 81 h in the binary mixture. Mechanism analysis found that the lag was mainly attributed to the exposure of DMS degrader (Alcaligenes sp. SY1), rather than PT metabolites and PT degrader. The exposure time and PT concentration also influenced the lag duration much. Citric acid could effectively reduce the lag. Pseudo-first-order model was proved suitable for the description of PT degradation, revealing that PT degradation could be enhanced in presence of DMS with a concentration of < 50 mg L-1. A modified Gompertz model, incorporated the lag phase, was developed for the description of DMS degradation in the mixture, revealing that DMS degradation depended on the initial PT concentration, and when the lag was not considered, PT with low-concentration could promote DMS biodegradation, while a higher concentration (> 20 mg L-1) cast negative effect.

Highly efficient removal of patulin using immobilized enzymes of Pseudomonas aeruginosa TF-06 entrapped in calcium alginate beads

Patulin is a toxic secondary metabolite produced by several moulds, which contaminates fruits and their products posing serious threats to human health. Though several microorganisms and enzymes have been reported to effectively degrade patulin, separation of them from fruit juice challenges the commercial applications. Here, a Pseudomonas aeruginosa strain TF-06 was isolated, its patulin degradation mechanism and optimum conditions for enzyme immobilization were investigated. The results indicated that TF-06 could degrade patulin into non-cytotoxic E/Z-ascladiol mainly by the activity of intracellular enzymes. For easy separation of enzymes, calcium alginate was selected for immobilization of intracellular enzymes from TF-06. The immobilized enzyme beads were effective in detoxification of patulin in apple juice. The mitigation rate was reached 95%, while there was no negative effect on juice quality. The study provides a promising way to resolve the issue of enzyme separation during mycotoxin biological detoxification in fruit juice.

Bacterial communities and their bioremediation capabilities in oil-contaminated agricultural soils

Rapid industrialization and development in petrochemical industries have resulted in increased hydrocarbon pollution causing substantial damage to the natural ecosystems including agricultural soils. In the recent, past efforts have been made to treat the contaminated soils using microorganisms by natural processes. Soil bacteria, known for their potential to degrade the soil contaminants, play a vital role in maintaining soil health. In the current study, we observed the influence of hydrocarbon contamination on the physicochemical characteristics and enzymatic activities of the soil. Proteobacteria (30.48%), Actinobacteria (13.91%), and Acidobacteria (12.57%) flourished in the non-contaminated soil whereas contaminated sites were dominated by Proteobacteria (44.02 ± 15.65%). In contrast, the sites experiencing the different degrees of exposure to the hydrocarbon pollution allowed specific augmentation of bacterial taxa (in decreasing order of exposure time), viz. Proteobacteria (60.47%), Firmicutes (32.48%), and Bacteroidetes(13.59%), based on culture-independent approach that suggested their potential role in hydrocarbon degradation as compared to the non-contaminated site. The imputation of metabolic function also supported the positive correlation to the exposure to hydrocarbon pollution, with site 2 being highly abundant for gene families involved in xenobiotics biodegradation. The study provides insights into bacterial community structure with special emphasis on their efficiency to degrade hydrocarbons. The results from the study can help in designing appropriate biodegradation strategies to mitigate the serious problems of oil contamination in agricultural soil.

Ambient Air Pollution Shapes Bacterial and Fungal Ivy Leaf Communities

Ambient air pollution exerts deleterious effects on our environment. Continuously exposed to the atmosphere, diverse communities of microorganisms thrive on leaf surfaces, the phylloplane. The composition of these communities is dynamic, responding to many environmental factors including ambient air pollution. In this field study, over a 2 year period, we sampled Hedera helix (ivy) leaves at six locations exposed to different ambient air pollution conditions. Daily, we monitored ambient black carbon (BC), PM_2.5, PM₁₀, nitrogen dioxide, and ozone concentrations and found that ambient air pollution led to a 2–7-fold BC increase on leaves, the phylloplane BC load. Our results further indicated that the phylloplane BC load correlates with the diversity of bacterial and fungal leaf communities, impacting diversity more than seasonal effects. The bacterial genera Novosphingobium, Hymenobacter, and Methylorubrum, and the fungal genus Ampelomyces were indicators for communities exposed to the highest phylloplane BC load. Parallel to this, we present one fungal and two bacterial phylloplane strains isolated from an air-polluted environment able to degrade benzene, toluene, and/or xylene, including a genomics-based description of the degradation pathways involved. The findings of this study suggest that ambient air pollution shapes microbial leaf communities, by affecting diversity and supporting members able to degrade airborne pollutants.

Characterization of lipopeptide biosurfactant produced by a carbazole-degrading bacterium Roseomonas cervicalis: The role of biosurfactant in carbazole solubilisation

AIM

Characterization of biosurfactant produced by a carbazole-degrading bacterium Roseomonas cervicalis and proteomic analysis of intracellular proteins of bacterium while growing on glucose and carbazole medium.

METHODS AND RESULTS

The bacterium R. cervicalis was isolated from a soil sample contaminated with crude petroleum oil. PCR amplification ascertained the existence of some hydrocarbon-degrading catabolic genes (alkB and PAH-RHDα, C12O, and C23O) in the bacterial genome. GC-MS and RP-HPLC analyses demonstrated 62% and 60% carbazole degradation, respectively, by R. cervicalis 144 h post-incubation at 37℃ and pH 6.5. Due to the paucity of protein databases, expressions of only 29 and 14 intracellular proteins were explicitly recognized and quantitated by mass spectrometry analysis when R. cervicalis was grown in carbazole and glucose medium, respectively. FTIR, NMR and HR-MS/MS analyses demonstrated the lipopeptide nature of the purified biosurfactant produced by R. cervicalis. The biosurfactant is also presumed to assist in the solubilization of carbazole.

CONCLUSION

The isolated R. cervicalis strain is a potential candidate for the bioremediation of carbazole in petroleum-oil-contaminated sites.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report of the promising R. cervicalis strain proficient in carbazole biodegradation.

Advances in engineered Bacillus subtilis biofilms and spores, and their applications in bioremediation, biocatalysis, and biomaterials

Bacillus subtilis is a commonly used commercial specie with broad applications in the fields of bioengineering and biotechnology. B. subtilis is capable of producing both biofilms and spores. Biofilms are matrix-encased multicellular communities that comprise various components including exopolysaccharides, proteins, extracellular DNA, and poly-γ-glutamic acid. These biofilms resist environmental conditions such as oxidative stress and hence have applications in bioremediation technologies. Furthermore, biofilms and spores can be engineered through biotechnological techniques for environmentally-friendly and safe production of bio-products such as enzymes. The ability to withstand with harsh conditions and producing spores makes Bacillus a suitable candidate for surface display technology. In recent years, the spores of such specie are widely used as it is generally regarded as safe to use. Advances in synthetic biology have enabled the reprogramming of biofilms to improve their functions and enhance the production of value-added products. Globally, there is increased interest in the production of engineered biosensors, biocatalysts, and biomaterials. The elastic modulus and gel properties of B. subtilis biofilms have been utilized to develop living materials. This review outlines the formation of B. subtilis biofilms and spores. Biotechnological engineering processes and their increasing application in bioremediation and biocatalysis, as well as the future directions of B. subtilis biofilm engineering, are discussed. Furthermore, the ability of B. subtilis biofilms and spores to fabricate functional living materials with self-regenerating, self-regulating and environmentally responsive characteristics has been summarized. This review aims to resume advances in biological engineering of B. subtilis biofilms and spores and their applications.

Statistical Optimisation of Diesel Biodegradation at Low Temperatures by an Antarctic Marine Bacterial Consortium Isolated from Non-Contaminated Seawater

Hydrocarbon pollution is widespread around the globe and, even in the remoteness of Antarctica, the impacts of hydrocarbons from anthropogenic sources are still apparent. Antarctica’s chronically cold temperatures and other extreme environmental conditions reduce the rates of biological processes, including the biodegradation of pollutants. However, the native Antarctic microbial diversity provides a reservoir of cold-adapted microorganisms, some of which have the potential for biodegradation. This study evaluated the diesel hydrocarbon-degrading ability of a psychrotolerant marine bacterial consortium obtained from the coast of the north-west Antarctic Peninsula. The consortium’s growth conditions were optimised using one-factor-at-a-time (OFAT) and statistical response surface methodology (RSM), which identified optimal growth conditions of pH 8.0, 10 °C, 25 ppt NaCl and 1.5 g/L NH₄NO₃. The predicted model was highly significant and confirmed that the parameters’ salinity, temperature, nitrogen concentration and initial diesel concentration significantly influenced diesel biodegradation. Using the optimised values generated by RSM, a mass reduction of 12.23 mg/mL from the initial 30.518 mg/mL (4% (w/v)) concentration of diesel was achieved within a 6 d incubation period. This study provides further evidence for the presence of native hydrocarbon-degrading bacteria in non-contaminated Antarctic seawater.

Biodegradation of aflatoxin by bacterial species isolated from poultry farms

Aflatoxins are carcinogenic compounds produced by certain Aspergillus spp and naturally contaminate poultry rations. Exposure to low levels of Aflatoxin B1 (AFB1) in poultry feeds is the second most threatening issue facing the poultry industry in Egypt; it can cause a reduction in growth, egg production, and compromised immune functions, resulting in significant economic loss. Hence, a safe, effective and eco-friendly detoxification method is strongly required. Biological decontamination is a promising approach to reduce aflatoxin levels within threshold limits. This study explores the biodegradation capacity of bacteria isolated from the moldy feed, soil and poultry feces in various poultry farms against AFB1 (100 ppb), G1 (100 ppb), B2 (30 ppb), G2 (30 ppb). Sixty-five bacterial isolates were initially screened using coumarin media with a concentration of (0.01%-0.5%) coumarin. Only one soil isolate (SZ1) grew at the highest concentration (0.5%). Coumarin and Aflatoxin degradation rates of ten promising isolates were measured using spectrophotometry and HPLC. Six isolates reduced AFG1 by more than 90% in the liquid medium, five reduced AFB2 while only four did the same with AFB1& AFG2. Impressively, isolate SZ1 (identified as Pseudomonas fluorescens) exhibited the best degradation capacity to both coumarin and aflatoxin with 100% degradation of AFG1 and 99% degradation of AFB1, AFB2 and AFG2. Biochemical and molecular identification of the ten isolates revealed that they belong to four genera; Bacillus (6), Pseudomonas (2), Enterococcus (1) and Stenotrophomonas (1). Factors affecting Pseudomonas fluorescens SZ1 degradation activity was further investigated. Optimum temperature, time and pH for maximum aflatoxin degradation were at 37 °C, 72 h and 7, respectively. Treatment with proteinase K reduced the degradation activity of G1 (31% ± 1.438), B1 (42% ± 1.438), G2 (19% ± 1.097), and B2 (25% ± 1.732), suggesting that the effective component in aflatoxin degradation may be protein in nature. Our study suggests the biocontrol potential of several different species isolated from poultry farms; B. haynesii, B. licheniformis, B. tequilensis, B. subtilis, B. amyloliquefaciens, Pseudomonas fluorescens, Enterococcus casseliflavus, and Stenotrophomonas maltophilia. The results proposed Pseudomonas fluorescens SZ1 as an excellent candidate for bioremediation and decontamination of aflatoxin in feed matrices. To the best of our knowledge, this is the first report identifying B. haynesii, Enterococcus casseliflavus, B. tequilensis and B. amyloliquefaciens with aflatoxin degradation activity.

BTEX biodegradation by Bacillus amyloliquefaciens subsp. plantarum W1 and its proposed BTEX biodegradation pathways

Benzene, toluene, ethylbenzene and (p-, m- and o-) xylene (BTEX) are classified as main pollutants by several environmental protection agencies. In this study, a non-pathogenic, Gram-positive rod-shape bacterium with an ability to degrade all six BTEX compounds, employed as an individual substrate or as a mixture, was isolated. The bacterial isolate was identified as Bacillus amyloliquefaciens subsp. plantarum strain W1. An overall BTEX biodegradation (as individual substrates) by strain W1 could be ranked as: toluene > benzene, ethylbenzene, p-xylene > m-xylene > o-xylene. When presented in a BTEX mixture, m-xylene and o-xylene biodegradation was slightly improved suggesting an induction effect by other BTEX components. BTEX biodegradation pathways of strain W1 were proposed based on analyses of its metabolic intermediates identified by LC–MS/MS. Detected activity of several putative monooxygenases and dioxygenases suggested the versatility of strain W1. Thus far, this is the first report of biodegradation pathways for all of the six BTEX compounds by a unique bacterium of the genus Bacillus. Moreover, B. amyloliquefaciens subsp. plantarum W1 could be a good candidate for an in situ bioremediation considering its Generally Recognized as Safe (GRAS) status and a possibility to serve as a plant growth-promoting rhizobacterium (PGPR).

Degradation of BTEX mixture by a new Pseudomonas putida strain: role of the quorum sensing in the modulation of the upper BTEX oxidative pathway

A new Pseudomonas putida strain (AQ8) was isolated from a decommissioned oil refinery's soil in Italy and characterized for its ability to degrade BTEX. The draft genome of the new strain was sequenced and annotated for genes that encode enzymes putatively involved in BTEX degradation and quorum sensing. The strain was transformed with a plasmid expressing lactonase, which cleaves the autoinducer quorum sensing signal molecule, the acyl-homoserine lactone, to obtain a quorum sensing minus strain. P. putida AQ8 depleted the 40% on average of all the components of the initial BTEX concentration in 36 h. The quorum sensing minus strain, in the same time interval, depleted only the 10% of the initial BTEX concentration. The role of quorum sensing in regulating the expression of the annotated benzene/toluene dioxygenase gene (benzA) and biphenyl/toluene/benzene dioxygenase (bphA) genes, which are involved in BTEX degradation, was studied by quantitative RT-real-time quantitative (q)PCR analysis. The qPCR data showed decreased levels of expression of the benzA and bphA genes in the quorum sensing minus strain. Our results showed, for the first time, quorum sensing modulation of the level of transcription of dioxygenase genes in the upper BTEX oxidation pathway.

Biodegradation of Polystyrene by Pseudomonas sp. Isolated from the Gut of Superworms (Larvae of Zophobas atratus)

Recently, various attempts have been made to solve plastic waste problems, such as development of biodegradation without producing pollution. Polystyrene (PS) is the fifth most used plastic in many industries; therefore, degrading PS becomes a critical global issue. Here, we reported Pseudomonas aeruginosa strain DSM 50071, initially isolated from the gut of the superworms, Zophobas atratus, and the PS degradation by Pseudomonas sp. DSM 50071. We examined PS degradation using electronic microscopy and measured changes in atomic composition and contact angles with water droplets on the PS surface that represents a chemical change from hydrophobicity to hydrophilicity. We have further examined chemical structural changes using X-ray photoelectron spectroscopy, Fourier-transform-infrared spectroscopy, and nuclear magnetic resonance (NMR) to confirm the formation of carbonyl groups (C═O) in the oxidation pathway during PS biodegradation. In reverse transcription quantitative polymerase chain reaction analysis, the gene expression level of serine hydrolase (SH) in Pseudomonas sp. DSM 50071 was highly increased during PS degradation, and the enzyme-mediated biodegradation of PS was further confirmed by the SH inhibitor treatment test. Thus, the significance of these findings goes beyond the discovery of a novel function of Pseudomonas sp. DSM 50071 in the gut of superworms, highlighting a potential solution for PS biodegradation.

Combination of highly efficient microflora to degrade paint spray exhaust gas

Spray paint exhaust gas contains recalcitrant volatile organic compounds (VOCs), such as benzene, toluene and xylene (BTX). Treating BTX with a biofilter often achieves unsatisfactory results because the biofilter lacks efficient microbial community. In this work, three strains for BTX degradation were isolated and identified as Pseudomonas putida, Bacillus cereus and Bacillus subtilis by using 16S rRNA sequencing technology. A consortium of highly efficient microbial community was then constructed on a stable biofilm to treat BTX in a biofilter. A relatively suitable ratio of P. putida, B. cereus and B. subtilis was obtained. An efficiency of over 90% was achieved in the biofilter with VOC concentration of 1000 mg/m3 through inoculation with the microbial community after only 10 days of operation. Thus, fast start-up of the biofilter was realised. Analysis of intermediate products by gas chromatography-mass spectrometry indicated that BTX was degraded into short-chain aldehydes or acids via ring opening reactions.

Kinetics of hydrocarbon degradation by a newly isolated heavy metal tolerant bacterium Novosphingobium panipatense P5:ABC

This study report kinetics of PAHs and crude oil degradation by a newly isolated multiple heavy metal tolerant Novosphingobium panipatense P5:ABC. The isolate showed hydrocarbon degrading enzyme activities namely alkane hydroxylase, catechol 1,2-dioxygenase and catechol 2,3-dioxygenase. The level of C23O activity was 9.63 times higher than C12O thus suggesting active involvement of meta-cleavage pathway. The data of biodegradation of hydrocarbons fitted well to the first order kinetic model. The degradation rate was highest for phenanthrene followed by crude oil, and fluoranthene. We have further reported the estimate of fundamental kinetic parameters, half-saturation constant (K_s) and maximum degradation rates (V_max) for biodegradation of phenanthrene and fluoranthene. Overall characterization underscores the potential of Novosphingobium in bioremediation of crude oil polluted sites.

Bioremediation of benzene-contaminated groundwater by calcium peroxide (CaO2) nanoparticles: Continuous-flow and biodiversity studies

Calcium peroxide (CaO₂) nanoparticles have been extensively applied in treatment of contaminated groundwater through bioremediation or modified Fenton (MF) processes. In the present study utilization of CaO₂ in bioremediation and MF (CaO₂+FeSO₄) reaction is investigated for benzene (50 mg/L) removal in continuous flow sand-packed columns. The results indicated that MF produced OH radicals markedly increased benzene remediation at first 30 days (up to 93%). But, OH generation rate was gradually declined when the pH was increased and finally 75% of initial benzene removed after 100d. In bioremediation column, because of supplying adequate oxygen by CaO₂, the number of planktonic bacteria logarithmically increased to more than 5 × 10⁶ CFU/mL (two orders of magnitude) and consequently 100% benzene removal was achieved by the end of experiment. Scanning electron microscopy analysis visualized the attached biofilm growth on sand surfaces in CaO₂ injected columns indicating their key role in the remediation process. The impact of each process on the microbial biodiversity of groundwater was investigated by next generation sequencing (NGS) of the 16S rRNA gene. The alpha and beta analysis indicated that microbial diversity is decreased by CaO₂ injection while benzene-degrading species such as Silanimonas, Arthrobacter and Pseudomonas spp. were dominated in remediation column.

Assessment of benzene, toluene, ethyl-benzene, and xylene (BTEX) toxicity in soil using sulfur-oxidizing bacterial (SOB) bioassay

The assessment of benzene, toluene, ethyl-benzene, and xylene (BTEX)-contaminated soil toxicity was performed using a sulfur-oxidizing bacteria (SOB) assay. The experiments were set up using an individual pollutant in a 25-mL bottle sealed with a rubber stopper and aluminum cap since BTEX are volatile. A large headspace volume (14 mL) was kept in the reactors to provide enough oxygen for the SOB. Soil samples were spiked with BTEX compounds in the concentration range of 1-1000 mg/kg. In reactors without BTEX compounds, approximately 85% of the theoretically required oxygen was consumed. Whereas, the reactors with benzene consumed in the range of 82-64% (5-100 mg/kg), those with toluene consumed 76-53% (1-50 mg/kg), those with ethyl-benzene consumed 44-71% (5-100 mg/kg), and those with xylene consumed 64-71% (1-10 mg/kg) of the theoretically required oxygen. The effective concentrations responsible for 50% growth inhibition (EC₅₀) for benzene, toluene, ethyl-benzene, and xylene detection were 130.2, 1.2, 15.2, and 0.7 mg/kg, respectively. These results suggest that this SOB-based bioassay can detect BTEX pollutants in soils.

Kinetic analysis and degradation mechanism for natural attenuation of xylenes under simulated marine conditions

Microcosm experiments were conducted to examine the attenuation of selected chemicals, i.e. m-xylene (MX), o-xylene (OX) and p-xylene (PX), under simulated marine conditions. Natural attenuation and the contribution of oxidation, photodegradation, biodegradation and volatilization to total attenuation were evaluated. The development of attenuation was in agreement with pseudo-first-order kinetics for all xylenes. The half-lives of MX, OX, and PX under optimal conditions were 0.76, 0.74 and 0.88 days, respectively. Attenuation kinetics were proposed to analyze the natural attenuation of xylenes. The leading attenuation type of MX, OX, and PX was volatilization, and the attenuation rate constants (K_V) were 0.5587, 0.6733, and 0.4821 d^-1, respectively. Biodegradation of OX (K_b: 0.0003 d^-1) was extremely inhibited. The attenuation kinetics presented the attenuation of xylenes in microcosm. The reaction kinetics could be applied to analyze the natural attenuation of chemicals. MX and OX can be converted to one another under certain conditions. Toluene and ethylbenzene were detected for OX in the OP (oxidation and photodegradation) experiment under simulated marine conditions. 4-Methylbenzyl alcohol, p-methyl benzaldehyde and p-toluic acid, as the major intermediates, were identified during the natural attenuation of PX using GC/MS.

Natural attenuation of naphthalene along the river-bank infiltration zone of the Liao River, Shenyang, China

In this study, the natural attenuation of naphthalene during riverbank infiltration was examined using batch experiments. The results indicated that, as the grain size and the permeability coefficient decreased, the natural attenuation rate of naphthalene increased, and it was highest in loam (62%) and lowest in coarse sand (20%). The half-life of naphthalene was longest in coarse sand (700 d) and shortest in mild clay (250 d). Facultative anaerobes such as Methylophilaceae accounted for about 70% of the total bacteria and played a major role in naphthalene degradation. A high total organic carbon concentration and large specific surface area can promote natural attenuation of naphthalene. Moreover, the adsorption to riverbank sediment in the hyporheic zone and bioremediation by indigenous microorganisms can effectively eliminate naphthalene during river water infiltration to the riverbank aquifer.

Application of magnesium peroxide (MgO2) nanoparticles for toluene remediation from groundwater: batch and column studies

In the present study, magnesium peroxide (MgO₂) nanoparticles were synthesized by electro-deposition process and characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The batch experiments were conducted to evaluate the MgO₂ half-life (600 mg/L) in groundwater under various temperatures (4, 15, and 30 °C) and initial pH (3, 7, and 12). The effect of Fe²⁺ ions (enhanced oxidation) on the toluene remediation by MgO₂ was also investigated. Nanoparticles were injected to sand-packed continuous-flow columns, and toluene removal (50 ppm) was studied within 50 days at 15 °C. The results indicated that the half-life of MgO₂ at pH 3 and 12 were 5 and 15 days, respectively, in comparison to 10 days at the initial pH 7 and 15 °C. The nanoparticles showed 20 and 7.5 days half-life at 4 and 30 °C temperatures, respectively. Injection of Fe²⁺ ions indicated an impressive effect on toluene removal by MgO₂, and the contaminant was completely removed after 5 and 10 days, in the batch and column experiments, respectively. Confocal laser scanning microscope (CLSM) analysis indicated that the attached biofilm had a significant role in the decontamination of groundwater. Comparison of bioremediation and enhanced oxidation resulted in a considerable insight into the application of magnesium peroxide in groundwater remediation. Graphical abstract ᅟ.

Sulfur dioxide and o-xylene co-treatment in biofilter: Performance, bacterial populations and bioaerosols emissions

Sulfur dioxide (SO₂) and benzene homologs are frequently present in the off-gas during the process of sewage sludge drying. A laboratory scale biofilter was set up to co-treat SO₂ and o-xylene in the present study. SO₂ and o-xylene could be removed simultaneously in a single biofilter. Their concentration ratio in the inlet stream influenced the removal efficiencies. It is worth noting that the removal of SO₂ could be enhanced when low concentrations of o-xylene were introduced into the biofilter. Pseudomonas sp., Paenibacillus sp., and Bacillus sp. were the main functional bacteria groups in the biofilter. Sulfur-oxidizing bacteria (SOB) and o-xylene-degrading bacteria (XB) thrived in the biofilter and their counts as well as their growth rate increased with the increase in amount of SO₂ and o-xylene supplied. The microbial populations differed in counts and species due to the properties and components of the compounds being treated in the biofilter. The presence of mixed substrates enhanced the diversity of the microbial population. During the treatment process, bioaerosols including potentially pathogenic bacteria, e.g., Acinetobacter lwoffii and Aeromonas sp., were emitted from the biofilter. Further investigation is needed to focus on the potential hazards caused by the bioaerosols emitted from waste gas treatment bioreactors.

Label-Free Proteomics of a Defined, Binary Co-culture Reveals Diversity of Competitive Responses Between Members of a Model Soil Microbial System

Interactions among members of microbial consortia drive the complex dynamics in soil, gut, and biotechnology microbiomes. Proteomic analysis of defined co-cultures of well-characterized species provides valuable information about microbial interactions. We used a label-free approach to quantify the responses to co-culture of two model bacterial species relevant to soil and rhizosphere ecology, Bacillus atrophaeus and Pseudomonas putida. Experiments determined the ratio of species in co-culture that would result in the greatest number of high-confidence protein identifications for both species. The 281 and 256 proteins with significant shifts in abundance for B. atrophaeus and P. putida, respectively, indicated responses to co-culture in overall metabolism, cell motility, and response to antagonistic compounds. Proteins associated with a virulent phenotype during surface-associated growth were significantly more abundant for P. putida in co-culture. Co-culture on agar plates triggered a filamentous phenotype in P. putida and avoidance of P. putida by B. atrophaeus colonies, corroborating antagonistic interactions between these species. Additional experiments showing increased relative abundance of P. putida under conditions of iron or zinc limitation and increased relative abundance of B. atrophaeus under magnesium limitation were consistent with patterns of changes in abundance of metal-binding proteins during co-culture. These results provide details on the nature of interactions between two species with antagonistic capabilities. Significant challenges remaining for the development of proteomics as a tool in microbial ecology include accurate quantification of low-abundance peptides, especially from rare species present at low relative abundance in a consortium.

Environmental behavior and eco-toxicity of xylene in aquatic environments: A review

With the demand for chemicals and fuels increasing continuously, the occurrence of accidental leakage poses great risks to the aquatic environment. Xylene, a hazardous and noxious substance, has been major concerns with regard to heterogeneity and eco-toxicity towards aquatic organisms. This review focused on the ecotoxicological hazards of m-, o-, and p-xylene, as well as mixed xylene, on aquatic organisms. The mechanism of action of xylenes was also demonstrated in details. The purpose of this review was to further understand transfer and diffusion of toxicity on marine and freshwater organisms of xylene in the aquatic environment. Another aim was to screen sensitive biomarkers which were suitable for ecotoxicological assessment and monitoring in an aquatic system.

Biodegradation of Diesel, Crude Oil and Spent Lubricating Oil by Soil Isolates of Bacillus spp

Two species of Bacillus, B. thuringiensis B3 and B. cereus B6, isolated from crude oil-contaminated sites in Ecuador, were tested for their capability in degrading polycyclic aromatic hydrocarbons (PAHs) in diesel (shake-flask), and to remove total petroleum hydrocarbons (TPHs) from crude oil- or spent lubricating oil-polluted soils (plot-scale). TPHs and PAHs were analyzed by Gas chromatography-Flame ionization detector (GC-FID) and High performance liquid chromatography (HPLC), respectively. Degradation percentages of PAHs by strain B6 were in the range of 11-83 after 30 days. A mixed culture of both the strains removed 84% and 28% of TPHs from crude oil- and spent lubricating oil-polluted soils, respectively. Reduction in the abundance of total n-alkane fractions (C₈-C₄₀) of spent lubricating oil was 94%, which was 18% higher than the control. Our results clearly indicate that the selected strains have great potential in degrading petroleum hydrocarbons at both laboratory- and field-scales.

Biodegradation of crude oil by a defined co-culture of indigenous bacterial consortium and exogenous Bacillus subtilis

The aim of this work was to study biodegradation of crude oil by defined co-cultures of indigenous bacterial consortium and exogenous Bacillus subtilis. Through residual oil analysis, it is apparent that the defined co-culture displayed a degradation ratio (85.01%) superior to indigenous bacterial consortium (71.32%) after 7days of incubation when ratio of inoculation size of indigenous bacterial consortium and Bacillus subtilis was 2:1. Long-chain n-alkanes could be degraded markedly by Bacillus subtilis. Result analysis of the bacterial community showed that a decrease in bacterial diversity in the defined co-culture and the enrichment of Burkholderiales order (98.1%) degrading hydrocarbons. The research results revealed that the promising potential of the defined co-culture for application to degradation of crude oil.

A composite microbial agent containing bacterial and fungal species: Optimization of the preparation process, analysis of characteristics, and use in the purification for volatile organic compounds

Proper preservation of microbial activity over long periods poses a considerable challenge for pollutant biopurification. A composite microbial agent, mainly composed of bacteria and fungi isolated by the current research team, was constructed in this study and its performance in the removal of mixed waste gases (containing α-pinene, n-butyl acetate and o-xylene) was investigated. According to the removal efficiency in the first 24h and the response to starvation, the optimal ratio of selected carriers (activated carbon, wheat bran and sawdust) was found to be 1:2:1. In some cases of storages, the removal capability of the microbial agent was more than twice that of the suspension. Microbial analysis showed that the inoculated bacterial and fungal strains dominated the agent preparation and utilization. These results indicated that the agent has potential for use in biopurification of mixed waste gas, favoring the reduction of environmental passives and longer retention of microbial activity.

Kinetics of nutrient enhanced crude oil degradation by Pseudomonas aeruginosa AKS1 and Bacillus sp. AKS2 isolated from Guwahati refinery, India

Bacterial degradation of crude oil in response to nutrient treatments has been vastly studied. But there is a paucity of information on kinetic parameters of crude oil degradation. Here we report the nutrient stimulated kinetic parameters of crude oil degradation assessed in terms of CO2 production and oil removal by Pseudomonas aeruginosa AKS1 and Bacillus sp. AKS2. The hydrocarbon degradation rate of P. aeruginosa AKS1 in oil only amended sediment was 10.75 ± 0.65 μg CO2-C g(-1) sediment day(-1) which was similar to degradation rate in sediments with no oil. In presence of both inorganic N & P, the degradation rate increased to 47.22 ± 1.32 μg CO2-C g(-1) sediment day(-1). The half-saturation constant (Ks) and maximum degradation rate (Vmax) for P. aeruginosa AKS1 under increasing N and saturating P concentration were 13.57 ± 0.53 μg N g(-1) sediment and 39.36 ± 1.42 μg CO2-C g(-1) sediment day(-1) respectively. The corresponding values at increasing P and a constant N concentration were 1.60 ± 0.13 μg P g(-1) sediment and 43.90 ± 1.03 μg CO2-C g(-1) sediment day(-1) respectively. Similarly the degradation rate of Bacillus sp. AKS2 in sediments amended with both inorganic nutrients N & P was seven fold higher than the rates in oil only or nutrient only treated sediments. The Ks and Vmax estimates of Bacillus sp. AKS2 under increasing N and saturating P concentration were 9.96 ± 1.25 μg N g(-1) sediment and 59.96 ± 7.56 μg CO2-C g(-1) sediment day(-1) respectively. The corresponding values for P at saturating N concentration were 0.46 ± 0.24 μg P g(-1) sediment and 63.63 ± 3.54 μg CO2-C g(-1) sediment day(-1) respectively. The rates of CO2 production by both isolates were further stimulated when oil concentration was increased above 12.5 mg g(-1) sediment. However, oil degradation activity declined at oil concentration above 40 mg g(-1) sediment when treated with constant nutrient: oil ratio. Both isolates exhibited alkane hydroxylase activity but aromatic degrading catechol 1, 2-dioxygenase and catechol 2, 3-dioxygenase activities were shown by P. aeruginosa AKS1 only.

Biodegradation of fluoranthene by a newly isolated strain of Bacillus stratosphericus from Mediterranean seawater of the Sfax fishing harbour, Tunisia

A physico-chemical characterization of seawater taken from the fishing harbour of Sfax, Tunisia, revealed a contamination by organic and inorganic micropollutants. An aerobic marine halotolerant Bacillus stratosphericus strain FLU5 was isolated after enrichment on fluoranthene, a persistent and toxic polycyclic aromatic hydrocarbon (PAH). GC-MS analyses showed that strain FLU5 was capable of degrading almost 45 % of fluoranthene (100 mg l(-1)), without yeast extract added, after 30 days of incubation at 30 g l(-1) NaCl and 37 °C. In addition, the isolate FLU5 showed a remarkable capacity to grow on a wide range of aliphatic, aromatic and complex hydrocarbons. This strain could also synthesize a biosurfactant which was capable of reducing the surface tension of the cell-free medium, during the growth on fluoranthene. The biodegradative abilities of PAHs are promising and can be used to perform the bioremediation strategies of seawaters and marine sediments contaminated by hydrocarbons.

Microcosm-based interaction studies between members of two ecophysiological groups of bioemulsifier producer and a hydrocarbon degrader from the Indian intertidal zone

Isolates were obtained from intertidal zone site samples from all five western and one eastern coastal states of India and were screened. These ecophysiological groups of aerobic, mesophilic, heterotrophic, sporulating, and bioemulsifier-producing bacteria were from Planococcaceae and Bacillaceae. This is the first report of bioemulsifier production by Sporosarcina spp., Lysinibacillus spp., B. thuringiensis, and B. flexus. In this group, Solibacillus silvestris AM1 was found to produce the highest emulsification activity (62.5 %EI) and the sample that yielded it was used to isolate the ecophysiological group of non-bioemulsifier-producing, hydrocarbon-degrading bacteria (belonging to Chromatiales and Bacillales). These yielded hitherto unreported degrader, Rheinheimera sp. CO6 which was selected for the interaction studies (in a microcosm) with bioemulsifier-producing S. silvestris AM1. The gas chromatographic study of these microcosm experiments revealed increased degradation of benzene, toluene, and xylene (BTX) and the growth of Rheinheimera sp. CO6 in the presence of bioemulsifier produced by S. silvestris AM1. Enhancement of the growth of S. silvestris AM1 in the presence of Rheinheimera sp. CO6 was observed possibly due to reduced toxicity of BTX suggesting mutualistic association between the two. This study elucidates the presence and interaction between enhancers and degraders in a hydrocarbon-contaminated intertidal zone and contributes to the knowledge during application of the two in remediation processes.

Nicosulfuron application in agricultural soils drives the selection towards NS-tolerant microorganisms harboring various levels of sensitivity to nicosulfuron

The action mode of sulfonylurea herbicides is the inhibition of the acetohydroxyacid synthase (AHAS) required for the biosynthesis of amino acids valine and isoleucine in plants. However, this enzyme is also present in a range of non-targeted organisms, among which soil microorganisms are known for their pivotal role in ecosystem functioning. In order to assess microbial toxicity of sulfonylurea herbicide nicosulfuron (NS), a tiered microcosm (Tier I) to field (Tier II) experiment was designed. Soil bacteria harboring AHAS enzyme tolerant to the herbicide nicosulfuron were enumerated, isolated, taxonomically identified, and physiologically characterized. Results suggested that application of nicosulfuron drives the selection towards NS-tolerant bacteria, with increasing levels of exposure inducing an increase in their abundance and diversity in soil. Tolerance to nicosulfuron was shown to be widespread among the microbial community with various bacteria belonging to Firmicutes (Bacillus) and Actinobacteria (Arthrobacter) phyla representing most abundant and diverse clusters. While Arthrobacter bacterial population dominated community evolved under lower (Tier II) nicosulfuron selection pressure, it turns out that Bacillus dominated community evolved under higher (Tier I) nicosulfuron selection pressure. Different NS-tolerant bacteria likewise showed different levels of sensitivity to the nicosulfuron estimated by growth kinetics on nicosulfuron. As evident, Tier I exposure allowed selection of populations able to better cope with nicosulfuron. One could propose that sulfonylureas-tolerant bacterial community could constitute a useful bioindicator of exposure to these herbicides for assessing their ecotoxicity towards soil microorganisms.

Aerobic biodegradation of trichloroethylene and phenol co-contaminants in groundwater by a bacterial community using hydrogen peroxide as the sole oxygen source

Trichloroethylene (TCE) and phenol were often found together as co-contaminants in the groundwater of industrial contaminated sites. An effective method to remove TCE was aerobic biodegradation by co-metabolism using phenol as growth substrates. However, the aerobic biodegradation process was easily limited by low concentration of dissolved oxygen (DO) in groundwater, and DO was improved by air blast technique with difficulty. This study enriched a bacterial community using hydrogen peroxide (H2O2) as the sole oxygen source to aerobically degrade TCE by co-metabolism with phenol in groundwater. The enriched cultures were acclimatized to 2-8 mM H2O2 which induced catalase, superoxide dismutase and peroxidase to decompose H2O2 to release O2 and reduce the toxicity. The bacterial community could degrade 120 mg/L TCE within 12 days by using 8 mM H2O2 as the optimum concentration, and the TCE degradation efficiency reached up to 80.6%. 16S rRNA gene cloning and sequencing showed that Bordetella, Stenotrophomonas sp., Sinorhizobium sp., Variovorax sp. and Sphingobium sp. were the dominant species in the enrichments, which were clustered in three phyla: Alphaproteobacteria, Betaproteobacteria and Gammaproteobacteria. Polymerase chain reaction detection proved that phenol hydroxylase (Lph) gene was involved in the co-metabolic degradation of phenol and TCE, which indicated that hydroxylase might catalyse the epoxidation of TCE to form the unstable molecule TCE-epoxide. The findings are significant for understanding the mechanism of biodegradation of TCE and phenol co-contamination and helpful for the potential applications of an aerobic bioremediation in situ the contaminated sites.

Natural attenuation of 1,2,4-trichlorobenzene in shallow aquifer at the Luhuagang's landfill site, Kaifeng, China

The natural attenuation of 1,2,4-trichlorobenzene (1,2,4-TCB) in shallow aquifer was investigated at the Luhuagang's landfill site (LLS), where the subsoil and shallow aquifer have been contaminated by certain chemicals owning to a lack of protective structures and leachate collection systems. Batch natural attenuation experiments and molecular biology experiments were conducted to study the natural attenuation characteristics of 1,2,4-TCB, the relative contributions of the primary natural attenuation processes and the functional microorganisms degrading 1,2,4-TCB, respectively. The results indicated that the relationship between degradation rate and 1,2,4-TCB concentrations was in line with first-order decay kinetics, and the natural attenuation rate of 1,2,4-TCB in the three media followed the order silt>fine sand>medium sand, which was related to the size of the media and the microbial population. The relative contribution of adsorption to natural attenuation was 97.7%, 98.2%, and 95.7% in unsterilized silt, fine sand and medium sand, respectively, and that of biodegradation was 2.3%, 1.8%, and 4.3%, respectively. These properties are related to the characteristics of the pollutants and the specific conditions at the contaminated sites, such as the characteristics of the aquifer media and microbial communities. The functional microorganisms degrading 1,2,4-TCB at the site were proved to be primarily Pseudomonas sp. This study indicates the feasibility of bioremediation (bioaugmentation and biostimulation) by indigenous microorganisms to treat 1,2,4-TCB contamination at the site.

Dimethylamine biodegradation by mixed culture enriched from drinking water biofilter

Dimethylamine (DMA) is one of the important precursors of drinking water disinfection by-product N-nitrosodimethylamine (NDMA). Reduction of DMA to minimize the formation of carcinogenic NDMA in drinking water is of practical importance. Biodegradation plays a major role in elimination of DMA pollution in the environment, yet information on DMA removal by drinking water biofilter is still lacking. In this study, microcosms with different treatments were constructed to investigate the potential of DMA removal by a mixed culture enriched from a drinking water biofilter and the effects of carbon and nitrogen sources. DMA could be quickly mineralized by the enrichment culture. Amendment of a carbon source, instead of a nitrogen source, had a profound impact on DMA removal. A shift in bacterial community structure was observed with DMA biodegradation, affected by carbon and nitrogen sources. Proteobacteria was the predominant phylum group in DMA-degrading microcosms. Microorganisms from a variety of bacterial genera might be responsible for the rapid DMA mineralization.

Aflatoxin B₁ degradation by a Pseudomonas strain

Aflatoxin B1 (AFB1), one of the most potent naturally occurring mutagens and carcinogens, causes significant threats to the food industry and animal production. In this study, 25 bacteria isolates were collected from grain kernels and soils displaying AFB1 reduction activity. Based on its degradation effectiveness, isolate N17-1 was selected for further characterization and identified as Pseudomonas aeruginosa. P. aeruginosa N17-1 could degrade AFB₁, AFB₂ and AFM₁ by 82.8%, 46.8% and 31.9% after incubation in Nutrient Broth (NB) medium at 37 °C for 72 h, respectively. The culture supernatant of isolate N17-1 degraded AFB₁ effectively, whereas the viable cells and intra cell extracts were far less effective. Factors influencing AFB1 degradation by the culture supernatant were investigated. Maximum degradation was observed at 55 °C. Ions Mn²⁺ and Cu²⁺ were activators for AFB1 degradation, however, ions Mg²⁺, Li⁺, Zn²⁺, Se²⁺, Fe³⁺ were strong inhibitors. Treatments with proteinase K and proteinase K plus SDS significantly reduced the degradation activity of the culture supernatant. No degradation products were observed based on preliminary LC-QTOF/MS analysis, indicating AFB₁ was metabolized to degradation products with chemical properties different from that of AFB₁. The results indicated that the degradation of AFB₁ by P. aeruginosa N17-1 was enzymatic and could have a great potential in industrial applications. This is the first report indicating that the isolate of P. aeruginosa possesses the ability to degrade aflatoxin.

Isolation and characterization of atrazine mineralizing Bacillus subtilis strain HB-6

Atrazine is a widely used herbicide with great environmental concern due to its high potential to contaminate soil and waters. An atrazine-degrading bacterial strain HB-6 was isolated from industrial wastewater and the 16S rRNA gene sequencing identified HB-6 as a Bacillus subtilis. PCR assays indicated that HB-6 contained atrazine-degrading genes trzN, atzB and atzC. The strain HB-6 was capable of utilizing atrazine and cyanuric acid as a sole nitrogen source for growth and even cleaved the s-triazine ring and mineralized atrazine. The strain demonstrated a very high efficiency of atrazine biodegradation with a broad optimum pH and temperature ranges and could be enhanced by cooperating with other bacteria, suggesting its huge potential for remediation of atrazine-contaminated sites. To our knowledge, there are few Bacillus subtilis strains reported that can mineralize atrazine, therefore, the present work might provide some new insights on atrazine remediation.

Microbial diversity, community composition and metabolic potential in hydrocarbon contaminated oily sludge: prospects for in situ bioremediation

Microbial community composition and metabolic potential have been explored in petroleum-hydrocarbon-contaminated sludge of an oil storage facility. Culture-independent clone library-based 16S rRNA gene analyses revealed that the bacterial community within the sludge was dominated by the members of β-Proteobacteria (35%), followed by Firmicutes (13%), δ-Proteobacteria (11%), Bacteroidetes (10%), Acidobacteria (6%), α-Proteobacteria (3%), Lentisphaerae (2%), Spirochaetes (2%), and unclassified bacteria (5%), whereas the archaeal community was composed of Thermoprotei (54%), Methanocellales (33%), Methanosarcinales/Methanosaeta (8%) and Methanoculleus (1%) members. Methyl coenzyme M reductase A (mcrA) gene (a functional biomarker) analyses also revealed predominance of hydrogenotrophic, methanogenic Archaea (Methanocellales, Methanobacteriales and Methanoculleus members) over acetoclastic methanogens (Methanosarcinales members). In order to explore the cultivable bacterial population, a total of 28 resident strains were identified and characterized in terms of their physiological and metabolic capabilities. Most of these could be taxonomically affiliated to the members of the genera Bacillus, Paenibacillus, Micrococcus, Brachybacterium, Aerococcus, and Zimmermannella, while two strains were identified as Pseudomonas and Pseudoxanthomonas. Metabolic profiling exhibited that majority of these isolates were capable of growing in presence of a variety of petroleum hydrocarbons as sole source of carbon, tolerating different heavy metals at higher concentrations (≥1 mM) and producing biosurfactant during growth. Many strains could grow under a wide range of pH, temperature, or salinity as well as under anaerobic conditions in the presence of different electron acceptors and donors in the growth medium. Correlation between the isolates and their metabolic properties was estimated by the unweighted pair group method with arithmetic mean (UPGMA) analysis. Overall observation indicated the presence of diverse groups of microorganisms including hydrocarbonoclastic, nitrate reducing, sulphate reducing, fermentative, syntrophic, methanogenic and methane-oxidizing bacteria and Archaea within the sludge community, which can be exploited for in situ bioremediation of the oily sludge.

Genome analysis and physiological comparison of Alicycliphilus denitrificans strains BC and K601(T.)

The genomes of the Betaproteobacteria Alicycliphilus denitrificans strains BC and K601^T have been sequenced to get insight into the physiology of the two strains. Strain BC degrades benzene with chlorate as electron acceptor. The cyclohexanol-degrading denitrifying strain K601^T is not able to use chlorate as electron acceptor, while strain BC cannot degrade cyclohexanol. The 16S rRNA sequences of strains BC and K601^T are identical and the fatty acid methyl ester patterns of the strains are similar. Basic Local Alignment Search Tool (BLAST) analysis of predicted open reading frames of both strains showed most hits with Acidovorax sp. JS42, a bacterium that degrades nitro-aromatics. The genomes include strain-specific plasmids (pAlide201 in strain K601^T and pAlide01 and pAlide02 in strain BC). Key genes of chlorate reduction in strain BC were located on a 120 kb megaplasmid (pAlide01), which was absent in strain K601^T. Genes involved in cyclohexanol degradation were only found in strain K601^T. Benzene and toluene are degraded via oxygenase-mediated pathways in both strains. Genes involved in the meta-cleavage pathway of catechol are present in the genomes of both strains. Strain BC also contains all genes of the ortho-cleavage pathway. The large number of mono- and dioxygenase genes in the genomes suggests that the two strains have a broader substrate range than known thus far.